In the testing of wafer based semiconductor devices, probe cards are typically used to provide electrical interconnection between a testing system and the semiconductor wafer. An exemplary type of probe card often used in high speed applications is a blade probe card. In such probe cards, “blades” (which are typically coupled to, and supported by, a printed circuit board) carry signal and ground paths.
FIG. 1A depicts a conventional blade 100, and FIG. 1B depicts two blades 100 connected to printed circuit board 102. Referring specifically to FIG. 1A, blade 100 comprises a ceramic material, e.g., 96% alumina, with a microstripline on surface 100a. More specifically, signal path 100c and ground path 100b are provided on surface 100a. Ground path 100b is electrically connected to ground plane 102a at interface “I.” Signal path 100c is electrically connected, e.g., soldered, to probe needle 100d. Probe needle 100d is configured to probe a contact pad of a semiconductor device during testing thereof. For example, probe needle 100d may comprise tungsten, beryllium copper, or paliney 7.
As depicted in FIG. 1B, a plurality of blades 100 are placed on PCB in circular form. For purposes of explanation, only two blades 100 are depicted in FIG. 1B, but the approach is applicable to probe cards having any number of blades.
The bandwidth of such a system may be explained based on a complete closed circuit, and as such, the bandwidth of one single blade is not relevant in a practical application. As a result, three different angles, e.g., 7.5 degrees, 90 degrees, and 180 degrees, between the blades are simulated for existing structure of FIGS. 1A-1B. It is apparent that different angles will have different electric and magnetic field patterns that will result in different bandwidths. As expected, the 180 degree configuration has the lowest bandwidth and the case when the signal is closest to the ground (the 7.5 degree configuration) will have the widest bandwidth. FIG. 3 depicts a table that summarizes the results for a conventional blade card in the 7.5 degree, 90 degree, and 180 degree configuration with a conventional blade supplying the ground. As depicted in FIG. 3, with 90 degrees between the blades, the bandwidth at −1 dB is 3.3 GHz.